Q10010902- I have had the problem with ARC-1221x volume mounting and 10.5.6 upgrade. I have OS (reverted back to 10.5.5) installed on internal drive. I am getting errors when trying to run recommended driver update (132_81223). Tried to install with and without ext RAID connected, also tried to install as 'root' user. We got the following errors.
Install File:
/System/Library/Extensions/ArcMSR.kext/Contents/MacOS/ArcMSR
Status: ERROR

You can delete the following old driver directory in reinstall driver update (132_81223) package. /System/Library/Extensions/ArcMSR.kext. You can also install the driver update (132_81223) on the internal Mac HDD with Mac OS-X 10.5.6.